When my Mac is docked or connected to something that has an active gigabit ethernet connection (doesn't seem to matter which dock or dongle I use, I have a choice of three options in this regard), I would expect it to use that faster docked ethernet connection, rather than Wifi.

However I have found that it seems to still favor the Wifi all the time.

Example: Just now I started a backup to my networked Time Machine drive (which is a fileshare on my NAS). It said the backup would take three hours. I canceled that backup, turned off the Wifi on the Mac, and started the backup again, to the same location. No changes to anything except that I turned off Wifi. Now it says the backup will take less than 30 minutes. This behavior is very consistent and reproducible.

When I google search for the problem, everything says I should do this:- Open system preferences control panel.- Select "Network"- Select the "gear" icon flyout menu.- Select "set service order".- Move the ethernet connection to the top.

Yep, already done that. The ethernet options I've had plugged in before are at the top (and my current active one is the very top), and wifi is below those. It has been configured that way for ages. Doesn't seem to fix it. But that's as far as my Google searches seem to be able to take me.

Thanks for that suggestion. I don't believe I did anything on purpose to set up different locations, but I'll check. I'm assuming you're referring to this.

The other thing that Google searches told me was that if I had multiple wifi networks connected to the same LAN, it might get confused in the routing and might prioritize the Wifi because it thinks it's a more direct route. I don't think that's what's happening with me either, or at least, it shouldn't be.

The Wifi router that I'm using is also my house's DHCP server, and everything in the house plugs into the Wifi router's built-in ethernet switch. The cable modem is upstream from the Wifi router, and we don't use the Wifi that's built into the cable modem. There are other ethernet switches in various places in the house, but they're just dumb switches, not routers. Still, if the Mac can detect that there are some switches in the chain, and it's trying to be clever about it, it might indeed think that the Wifi is the shorter link... Between my Mac and the router, there are two gigabit-ethernet switches: One in my office/studio that the Mac is plugged into (along with all my other gear in the office), and one in the closet just before the Wifi router (the rest of the ethernet ports in the house connect to that switch in the closet too).

I might mention that a cable manufacturer can print whatever they want on the cable jacket. The printing doesn’t necessarily mean it meets the specs (or any specs). Lots of maybe, or maybe not, cables on the market.

Same goes for the wall jacks.

I also have seen more than a few where the cable termination at the wall jack was sub-standard, loose, corroded, or just plain flakey. Not to mention cables mis-wired at the jack, wrong pin color coding, etc.

Usually network interfaces will have a metric or priority e.g. route print will show in Windows or just route in Linux will show you. Mac being BSD based might be "netstat -r"

When you have two devices on the same subnet it should use the highest priority interface (usually the lowest number) when a new connection is created. Why Wi-Fi is prioritised is an Apple decision if that's what they're doing.

Also the other issue may be simply it already has a connection open via the Wi-Fi interface that it doesn't want to disconnect so it keeps using that. That should be fixed by stopping/restarting the backup or you could even try rebooting.

networksetup -listnetworkserviceorder- Lists the network service order. Should match what the GUI tells me.- It does indeed match what the GUI tells me.- Also it shows me that the ethernet interface is "en10" and the wifi interface is "en0"

nettop- Lists active data connections including which interface they're on.- So that I can confirm/deny my theory that the problem is due to usage of the wifi interface.

That last one is proving helpful. I'm currently seeing a mixture of connections, some on en10 and some on en0. The process names are sometimes clear, other times, not so much. I'm having trouble figuring out which processes are the ones that are the Time Machine backup process. I want to confirm/deny which one is the time machine backup so that I can be sure the slow backup is truly due to using the wifi.

Ah, the reason I couldn't tell which process was the backup process is because (a) it's called "kernel task 0" which is kinda weird for a backup process, and also, it hadn't made its connection yet. When it's at the "preparing backup..." stage, it hasn't yet made a connnection, so there's nothing on the chart yet.

Once it makes a connection, the nettop command shows that it's using the ethernet connection:

Actually very few tasks seem to use the "en0" wlan interface, and they kind of come and go randomly. Mostly it's just a DNS responder "listen" process, and Dropbox (which I don't understand really).

Anyway, full nettop output attached, but this destroys my assumption that it's related to interface priority.

My behavior that was originally stated is still true: Wifi on, slow backup, Wifi off, fast backup. But now I have to suspect, and begin to troubleshoot, the network routing, network cabling, gig switches, or wifi router.

Interface number being en0 or en10 should not be indicator of priority. It's a separate configuration.

Yep. Sorry for not making it clear in my post: I understand this, I was merely listing the interface ID's because the "nettop" command output doesn't show the friendly names, it only shows those IDs.

Reading back on the post, I can see how the post makes it look like I might have thought that the ID number was somehow a priority level. Thanks for making sure.

I haven't dug any farther into the problem since discovering, via the "nettop" command, that the backup process was definitely using the ethernet interface. I don't know why it's slower when wifi is enabled, but at least now I know that it's not an interface priority thing.